1. Field of the Invention
This disclosure relates in general to an isolation sleeve employed during hydraulic fracturing operations through production tubing to protect the wellhead from the high fracturing pressure, and in particular to a sleeve assembly that is adjustable in length to accommodate variation in different wellhead stack-ups and tolerances.
2. Description of Prior Art
One type of treatment for an oil or gas well is referred to as well fracturing or a well “frac”. In a typical tracing operation, an adapter is connected to the upper end of a wellhead member, and high pressure liquid is pumped down the well to create fractures in the earth formation. Proppant material is often included in the fracturing fluid, which enters the fractures to maintain them open alter the high pressure is removed. Hydraulic fracturing is particularly useful for hydrocarbon bearing earth formations with low permeability and adequate porosity, as the entrained hydrocarbons can flow more easily through the fractures created in the earth formation.
Fracing fluid pressure often ranges up to pressures of 8,000 to 9,000 psi; whereas normal wellhead operating pressure may be a few hundred to a few thousand psi. Accordingly, fracing pressures usually exceed pressure ratings of the wellhead and its associated valves. Moreover, additives to the frac fluid, such as the proppant, can be very abrasive and damaging to parts of the wellhead. Isolation sleeves are sometimes used to address the issues of overpressure and fluid erosion. Generally, isolation sleeves seal between an adapter above the wellhead and the casing or tubing extending into the well.